Antimony(V) fluoride, SbF5, forms a molecular adduct with pyrazine (1,4-diazine) of the composition 1,4-C4H4N2.2SbF5. Its molecular structure is obtained by single crystal X-ray diffraction. Crystal data of pyrazine.2SbF(5): orthorhombic, spacegroup Pbca (# 61); a = 8.8052(8) Angstrom; b = 9.948(1) Angstrom; c = 12.297(2) Angstrom; V = 1077.1(2) Angstrom(3); Z = 4; T = 173(1) K; R-1(I > 3sigma (I)) = 0.031; wR(2) = 0.083. The Sb-F-4(eq) planes are eclipsed and the planar C4H4N2 ring is at a 45degrees angle to give D-2h symmetry for pyrazine.2SbF(5). A very similar high symmetry conformation of pointgroup D-4h is found for the [Sb2F11](-) anion in the metal carbonyl salts [Rh(CO)(4)][Sb2F11], [Au(CO)(2)][Sb2F11] and in [H3F2][Sb2F11]. Structural data for pyrazine.2SbF(5) and [Sb2F11](-) from [H3F2][Sb2F11], as well as vibrational data for [Sb2F11](-) (D-4h) are compared to calculated (DFT-B3LYP) data. According to the DFT calculations, the conformation for the[Sb2F11](-) anion (D-4h) and pyrazine.2SbF(5) (D-2h) are both eclipsed with respect to the SbF5-groups and eclipsed with respect to the pyrazine plane in pyrazine.2SbF(5) in their respective ground states. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.